Evaluation of growth promoting implant strategies and days on feed on finishing heifer performance and evaluation of optimal reimplant times for finishing heifers and steers

Authors

Caitlin Ohnoutka, University of Nebraska–LincolnFollow

First Advisor

Galen E. Erickson

Date of this Version

Summer 8-2018

Comments

A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In partial Fulfillment of Requirements For the Degree of Master of Science, Major: Animal Science, Under the Supervision of Professor Galen E. Erickson. Lincoln, Nebraska: August 2018

Copyright © 2018 Caitlin A. Ohnoutka

Abstract

Two experiments evaluated the effects of delayed, long-acting coated implants or uncoated implants to non-implanted heifers fed for constant or varying days on feed. In Exp. 1, heifers were implanted with either Revalor-XH on d 1, Revalor-200 on d 1, Revalor-XR on d 1, or Revalor-200 on d 70 compared to non-implanted control heifers when fed for an average of 198 d. In Exp. 2, heifers were implanted with Revalor-200 on d 1 and reimplanted with Revalor-200 on d 100, Revalor-XH on d 1, or not implanted and fed for different days on feed: 151, 165, 179, or 193. Implanting heifers increased BW, ADG, G:F and HCW compared to non-implanted heifers with no differences between implant strategies. As heifers were fed for longer DOF, ADG and G:F decreased. Implanting and increasing DOF substantially increased BW and HCW but increasing initial implant dosage did not result in a performance advantage when heifers were fed for varying DOF.

Two experiments evaluated the effect of timing of administering a terminal implant in heifers and steers when fed for 180 days. In Exp. 3, heifers were implanted with Revalor-IH and reimplanted with Revalor-200 at 20, 60, 100 or 140 DOF. In Exp. 4, steers were implanted with Revalor-IS and reimplanted with Revalor-200 on 20, 60, 80, 100 or 140 DOF. In Exp. 3, final BW, ADG, G:F, HCW and LM area responded quadratically and were maximized between 88 and 103 on terminal (DOT) implant. In Exp. 4, carcass-adjusted final BW, ADG, G:F and HCW responded quadratically and was optimized between 87 and 104 DOT. Therefore, the optimal duration for a terminal implant appears to be between 80 and 120 DOT, with an average of 96 DOT for both heifers and steers.

Advisor: Galen E. Erickson